Electron Microscopy grids are used as supports for observing nanoparticles and biological molecules. Scanning Electron Microscopy (SEM) looks at the electrons scattered from the front of a sample and thus can observe thick samples. As opposed to SEM, Transmission ElectronMicroscopy (TEM) works by passing the electron beam though the sample AND the support. There are two types of TEMs—High-Resolution TEM (HRTEM or often abbreviated just TEM) and Scanning Transmission Electron Microscopy (STEM). In HRTEM, the electron beam is parallel at the sample. Contrast is obtained by changing the phase of the electrons and their interference with each other. In another form of TEM, Scanning TEM (STEM), the electron beam is focused at the surface to a fine spot. Contrast is obtained by scattering of the electrons from the atoms. The heaver the atom, the more the scattering. Electrons that do not scatter are often not analyzed.
In both HRTEM and STEM, since the electrons must pass though the support, the thinner the support the less contrast the support contributes to the total image. For the observation of particles <1 nm in diameter, i.e. a few atom layers thick, the ideal support would be vacuum. However, vacuum does not immobilize the particles, so atoms in the nanoparticle cannot often be imaged because they move and blur during the analysis.
Recently, graphene and graphene oxide supports have become commercially available as examples of thin supports being only one atom thick in ideal cases. However, these supports are often contaminated with carbon from either the preparation process or storage in air. This added carbon adds noise to the image due to its random nature. Additionally, graphene, being only one atom thick, is not robust from handling during sample deposition nor the electron beam during analysis. Thus, Ultrathin Carbon (UT) Type A (3-4 nm) with removable Formvar thick film of amorphous carbon is often employed to image nm size samples. UT carbon is typically prepared by evaporating carbon onto a flat surface such as mica, removing the mica by separating with water, and floating the UT carbon onto a grid or grid with a support. UT carbon has limitations in that it cannot be readily cleaned. Additionally, being carbon, the carbon is transferred to the sample during analysis by the electron beam, which changes the structure of the sample.
Silicon monoxide supports are commercially available but they are too thick for good HRTEM work. Additionally, they are not available commercially as supported films, so they previously could not be made very thin—until this invention solved this long standing problem.